Dry etching techniques, such as reactive ion etching, have become indispensable as fine pattern delineation techniques in very large scale integration (VLSI) fabrication. As a specific example, reactive ion etching involves ion bombardment of the surface being etched. As pattern densities increase and device dimensions shrink, it is important to tightly control the degree of isotropy or undercutting of etching profiles. During the etching of silicon, oxide or metal, gases which react in plasma such as chlorine, bromine or iodine containing gases, are typically used to generate low volatility etch products which deposit as passivating films on sidewalls in order to achieve anisotropic etch profiles. In addition, etch by-products also deposit onto the substrate and can terminate the etching when certain underlying materials are reached during the etching process.
As a specific example, fluorocarbon compounds are often used to etch insulator materials, such as silicon dioxide or silicon nitride. Carbon-polymers are deposited on the sidewalls of the etched region, and are also deposited when the etching proceeds to the underlying layer material. The underlying layer material may comprise, for example, silicon, silicide, or metals. Carbon-polymers deposit on these materials because the interaction of the fluorocarbon radicals with these materials produces fewer volatile by-products. This is also the case for sidewalls because ion bombardment less effectively initiates etching on these sloped surfaces. In both cases, the carbon-polymers inhibit continued etching.
The sidewall films and etch by-products allow reactive ion etching to be highly selective and to produce substantially anisotropic profiles. These sidewall films containing C, O, H, Cl, metals or other species are relatively thick, chemically resistant, and less exposed to ion bombardment during the etching. These films are also produced during plasma etching where substantially less ion bombardment is involved. In both types of etching, before subsequent processing can continue, these sidewall films and etch by-products must be removed. In some cases, such as in metal etching, the sidewall films contain chlorine compounds which cause the fine structure to corrode if they are not removed within a few hours. The sidewall films and etch by-products contain impurities which can adversely affect the success of subsequent processing and ultimately the electrical performance of the resulting devices.
Currently, the most widely implemented post-plasma-etch cleaning processes utilize RCA cleaning, chemical vapors and/or wet chemical etching, utilizing acids, such as dilute HF, H.sub.2 SO.sub.4 /H.sub.2 O.sub.2, and chromic acid. Disadvantageously, these techniques result in etching of thin surface films including silicon dioxide, silicide, metal, and cause undercut and lift-off of thin films. Degradation of the thin films becomes unacceptable as device dimensions continue to shrink. In addition, the wet chemical clean methods are unable to produce a substantially particle and residue free surface, which is critical for high yield device manufacturing.
U.S. Pat. No. 5,025,632 to Spritzer relates to a method and apparatus for removing a surface layer of energetic material, such as solid rocket propellants, explosives and pyrotechnic materials, contained within munition casings. Spritzer discloses utilizing a wand to direct a cryogenic fluid spray at the material in a dry washout process to freeze and embrittle the surface layer either by precooling and fluid spray, or by spray alone. However, the Spritzer method does not relate to and is incapable of removing sidewall films and etch by-products from delicate, fragile, and tightly spaced semiconductor structures.